This invention relates to fiberizing apparatuses and more particularly to fiberizing apparatuses which are capable of fiberizing wet or dry mats of fibers, such as wood pulp sheets or mats.
Fiberizing apparatuses exist for fiberizing wet or dry pulp mats.
A first type of known fiberizing apparatus uses a high speed propeller blade type device within an enclosed housing for fiberizing pulp mats. An example of such an apparatus is disclosed by U.S. Pat. No. 3,987,968. In a propeller type system there are a limited number of active fiberizing surfaces. This limited capability reduces the capacity of the fiberizer and makes the processing of multiple pulp mats impractical.
Another type of fiberizing apparatus employs a sawtooth shaped ripping blade helically mounted to the surface of a rotating cylinder. As a pulp mat is fed into the surface formed by the rotating blade, the blade progressively rips off fibers from the advancing mat. This apparatus suffers from the drawbacks of tearing the mat into large chunks which can wrap around the rotor. In addition, the teeth of this type of fiberizer tend to become filled with fibers, thus reducing its fiberizing capabilities.
In addition, known fiberizers or comminution machinery, when used to fiberize sheets treated with a crosslinking agent, result in the production of an excessive number of nits. Any curing of the crosslinking agent which occurs before the fibers are fiberized would cause interfiber bonding and thereby would contribute to nit formation. Such interfiber bonding would make any subsequent attempt at complete fiberization virtually impossible. Crosslinked cellulose fibers when used in many products cannot have excessive amounts of nits. Nits are hard, dense agglomerations of fibers held together by crosslinking agents due to the ability of crosslinking agents to covalently bond a number of individual fibers together. Nits can be defined as having a surface area of about 0.04 mm.sup.2 to about 2.00 mm.sup.2. A nit usually has a density greater than 0.8 g/cm.sup.3, with a density of about 1.1 g/cm.sup.3 being typical. It is virtually impossible to separate fibers comprising a nit from one another in a conventional communition device. As a result, these recalcitrant agglomerated fiber nits become incorporated into the final absorbent product where they can cause a substantial degradation of product aesthetic or functional quality. For example, nits can substantially reduce the absorbency, resiliency, and loft of an absorbent product. For aesthetically sensitive products, such as certain types of paper, the "nit level" of three or less (three or fewer nits per six-inch diameter test "hand sheet") may be regarded as a maximally acceptable number of nits. The occurrence of nits in filters using crosslinked fibers is particularly disadvantageous.
The fiberization devices (to effect "individualization" of fibers or separation of the fibers from one another) presently known to the inventors used in the prior art in connection with a fiberizing crosslink agent treated mats produce too many nits to be acceptable for many uses. This problem has been recognized in U.S. Pat. No. 3,440,135 to Chung, which discloses a process for crosslinking cellulose fibers comprising impregnating a mat of non-woven cellulose fibers and fiberizing the mat. Chung mentions the use of conventional fiberizing devices for this purpose and recites that an excessive number of nits are produced unless a pretreatment step is utilized. In Chung, this pretreatment step is described as "aging" the fiber mats following the application of a crosslinking agent for many hours. Chung mentions that this "aging" of crosslink agent treated mats overcomes the problem of excessive nit formation. This pretreatment "aging" process is extremely impractical due to the requirement of storing rolls of the crosslink agent treated mats. Thus, the Chung patent accepts the excessive nit formation caused by prior art fiberization machinery and attempts to overcome this problem by changing processing steps prior to fiberization of the material.
Therefore, a need exists for an improved fiberizing apparatus directed toward overcoming these and other disadvantages of the prior art and in particular one which minimizes nit formation when fiberizing pretreated fibers, such as fibers pretreated with a crosslinking agent.